The invention relates to a device for detaching a filter cake which adheres to a filter cloth of a filter press, comprising at least two deflection bodies around which the filter cloth extends in an S-shaped manner and which can be moved in an approximately vertical direction, so that the S-shaped deflection brushes essentially completely over the adhering area of the filter cake. Such a device has already been realized in the filter press for the filtration of suspensions as known from EP 0 718 020 A1. The deflection bodies are arranged in this case as two horizontally aligned rollers which are disposed at opposite sides of the filter cloth and are provided with a horizontal as well as vertical offset of their rotational shafts. Both rollers are combined into a module by way of coupling elements which are provided with laterally projecting carriers which enable all pairs of rollers to be simultaneously brought into engagement with a vertically movable lifting device and can thus be moved upwardly and downwardly.
Whereas the pairs of rollers are disposed below the filter plates in the compressed state of the filter plate packet, i.e. during the actual filtration process, the upward and downward movement of the pairs of rollers and thus the detachment of the filter cake occurs after the termination of the filtration process and the horizontal removal of adjacent filter plates to the so-called discharging distance.
A further development of the filter press as known from EP 0 718 020 A1 is described in DE 197 45 289 C1. In order to avoid the simultaneous lifting and lowering of all pairs of rollers, the lifting device which extends over the entire length of the filter press is provided with a driver carriage which is movable in the longitudinal direction of the filter plate and can be brought into engagement with merely a small number of filter plates. As a result, only the pairs of rollers of the filter plates brought previously to the mutual discharging distance can be lifted. The principal of the S-shaped deflection of the filter cloth with the help of two rollers has remained unchanged, however.
When applying the known principle of filter cake detachment it may occur, especially in cases where the cake is not completely filtered out or is adhesive, that parts of the cake will not detach from the filter cloth despite the comparably strong deflection in the zone of the rollers, as a result of which the build-up of a homogeneous filter cake can be impaired during a subsequent filtration process. Moreover, the degree of soiling of the filter cloths may increase by the potentially incomplete detachment of the filter cake, which requires the frequent application of a special cleaning device by using a pressurized cleaning liquid.
Furthermore, the cake residues adhering to the filter cloth are applied on the roller jacket of the inner roller during the lifting and lowering of the pairs of rollers.
The invention is based on the object of further developing the known detachment device in such a way that any adherence of cake residue on the filter cloth and on the deflection bodies is prevented.
Based on a device of the kind as described above, this object is achieved in accordance with the invention in such a way that the filter cloth extends in a sliding fashion during a relative movement between the same and the deflection bodies over a surface of at least one deflection body and is provided with a bend in its course at a longitudinal edge of said deflection body.
According to the invention, at least one deflection body is thus arranged in such a way that it fulfils both the function of the deflection of the filter cloth as well as the function of a scraper brushing over the filter cloth surface. As a result of the bend in the course of the filter cloth it is ensured that the filter cloth will rest securely on the longitudinal edge of the deflection body which performs the scraper function. The sliding of the filter cloth over the non-rotating deflection body in accordance with the invention ensures a relative movement between the scraper edge and the cloth, which forms a basic prerequisite for the achievement of the scraping effect.
As a result of providing a combined scraper and deflection element in accordance with the invention, the construction is characterized by low production costs, especially in comparison with a solution in which a scraper device is disposed as an additional component between the two rollers. Moreover, the need for space for the detachment device according to the invention is lower than in a construction with an additional scraper device.
Preferably, the deflection body which is the second one during the detaching process in the direction of movement of the cloth is provided in accordance with an embodiment of the invention with a longitudinal edge which produces a bend and faces the first deflection body.
It is ensured in this manner that the scraping effect is performed directly after a detachment of the main part of the filter cake on the first deflection body. This residual detachment with the help of the scraper occurs at a time before the filter cloth comes into contact with its side facing the filter cake with the deflection surfaces of the second deflection body, so that their soiling is minimized.
It is particularly favorable from a production viewpoint if the deflection body is a scraper plate which is C-shaped with respect to its cross section in its end section and is provided with a wedge angle which starts out from its longitudinal edge and is in the range of between 45xc2x0 and 90xc2x0.
In conjunction with the acute wedge angle, the C-shape of the scraper plate ensures a secure take-up and deflection of the scrape filter cake residue. The acute wedge angle represents in this connection a high efficiency of the scraper effect.
In a further development of the invention it is provided that the filter cloth is deflected in the zone of the longitudinal edge by an angle of between 2xc2x0 and 20xc2x0. This ensures a sufficiently reliable contact of the filter cloth on the longitudinal edge and still a protection of the filter cloth material.
It is further particularly preferable if the angle of wrap of the filter cloth about the scraper plate is between 60xc2x0 and 120xc2x0 and the scraper plate is provided with a thickness in the range of between 1 mm and 8 mm in a zone adjacent to the longitudinal edge.
It is further provided in accordance with the invention that both deflection bodies are rigidly connected with one another via coupling elements and can thus be lifted and lowered in a forced synchronized manner with the help of a lifting device.
The detaching device is only disposed on the filter plate side on which the filter cake remains adhering to the filter cloth. According to experience, this is the case with chamber filter plates.
A particularly advantageous further development of the device in accordance with the invention is that on each face side of every other filter plate two coupling elements each are flexibly connected with one another and can be brought jointly into engagement with the lifting device.
In this way the lifting device grasps two coupling elements simultaneously via a single carrier on each side of the filter plate and thus produces the cake detachment of a common filter cloth on both sides of a chamber plate. In this case it is not necessary that the membrane plates are provided with detaching devices.